ST. LOUIS (AP) -- A 3,200-year-old mummy mask at the center of a years-long custody fight will stay at the St. Louis Art Museum now that the U.S. government is giving up its fight to reclaim it for Egypt.

U.S. Attorney Richard Callahan said Tuesday that the Department of Justice will take no further legal action to reclaim the funeral mask of Lady Ka-Nefer-Nefer, a noblewoman who died in 1186 B.C.

The mask went missing from the Egyptian Museum in Cairo more than 40 years ago. The St. Louis Art Museum said it researched the provenance of the mask and legitimately bought it in 1998.

A federal judge ruled in 2012 that the U.S. government provided no evidence of "theft, smuggling or clandestine importation." An appeals court panel later agreed.

"We were relying on the lack of any records showing a lawful transfer," Callahan said. "The court ended up deciding that wasn't enough to lead to an inference of stealing."

A message seeking comment from Egypt's Supreme Council of Antiquities was not immediately returned Tuesday.

Museum attorney David Linenbroker applauded the decision, saying: "We believe that it received a full and fair proceeding, and we're glad that it's finally coming to an end."

The mask is 20 inches (50 centimeters) long, made of painted and gilded plaster-coated linen over wood with inlaid glass eyes. It was excavated from one of the Saqqara pyramids, south of Cairo, in 1952.

U.S. government investigators suspected that the mask was stolen sometime between 1966, when it was shipped to Cairo for an exhibit, and 1973, when the Egyptian Museum discovered it was missing.

The art museum bought the mask in 1998 for $499,000 from a New York art dealer. The museum's research showed that the mask was part of the Kaloterna private collection during the 1960s, before a Croatian collector, Zuzi Jelinek, bought it in Switzerland and later sold it to the dealer, Phoenix Ancient Art of New York, in 1995.

Egyptian officials began trying to get the mask back once they learned of its whereabouts in 2006. Negotiations failed, prompting the legal fight between the U.S. government and the art museum that began in 2011.